Registration method

ABSTRACT

A three-dimensional image is produced using an imaging medium having a lenticular screen, the lenticles of the screen dividing the opposed surface of the imaging medium into a plurality of elongate image areas, the imaging medium having on the opposed side thereof a radiation-sensitive layer, the radiation-sensitive layer comprising a color-forming composition adapted to undergo a change of color upon increase in the temperature of the radiation-sensitive layer above a color-forming temperature for a color-forming time. The radiation-sensitive layer is imagewise exposed to actinic radiation which does not pass through the lenticular screen, thereby causing the color-forming composition to undergo its change in color in exposed areas and to form in the radiation-sensitive layer a composite image, the composite image comprising, in each of the image areas, a plurality of image strips extending lengthwise along the image area, each of the image strips containing information from a view of the object, each of the plurality of image strips in one image area containing information from a different view of the object thereby forming a copy of the composite image in the radiation-sensitive layer, so that a three-dimensional orthoscopic image of the object will appear to an observer seeing the composite image in the radiation-sensitive layer through the lenticular screen.

This application is a division of application Ser. No. 07/881,125, filedMay 11, 1992 now U.S. Pat. No. 5,279,912.

REFERENCES TO RELATED APPLICATIONS

Copending application Ser. No. 07/695,641, filed May 6, 1991, describesand claims thermal imaging media having the bubble-suppressant layershown in FIG. 2 of the accompanying drawings.

Copending application Ser. No. 07/696,196, filed May 6, 1991, describesand claims thermal imaging media having a color-forming layer with ahigh glass transition temperature, and at least one diffusion-reducinglayer, as shown in FIG. 2 of the accompanying drawings.

U.S. Pat. No. 5,153,169 describes and claims imaging media having acolor-forming layer containing a hindered amine light stabilizer or anitrone as a color stabilizer, as used in the imaging medium shown inFIG. 2 of the accompanying drawings.

U.S. Pat. No. 5,231,190 describes and claims the infra-red dye offormula: ##STR1## used in the thermal imaging medium of the presentinvention shown in FIG. 2 of the accompanying drawings.

Copending application Ser. No. 07/277,014, filed Nov. 28, 1988,describes and claims the yellow leuco dye used in the thermal imagingmedium of the present invention shown in FIG. 2 of the accompanyingdrawings.

Copending application Ser. No. 07/795,038, filed Nov. 20, 1991,describes and claims certain bis(benzpyrylium) infra-red dyes, includingthe croconate dye used in the radiation-sensitive layer described belowwith reference to FIG. 2 of the accompanying drawings.

U.S. Pat. No. 5,227,408 describes and claims certain amino-substitutedsquarylium infra-red dyes, including the dyes of Formulae IR2, IR3 andIR5 used in the radiation-sensitive layer described below with referenceto FIG. 2 of the accompanying drawings.

The disclosures of all the aforementioned patents and copendingapplications are herein incorporated by reference.

BACKGROUND OF THE INVENTION

Modern computer drawing and modelling programs (usually known as"computer assisted design" or "CAD" programs) can display complicatedthree-dimensional objects in great detail, can generate shadows showingthe appearance of the object in various types and directions oflighting, and permit the observer to rotate the three-dimensional objectabout any axis, so that he can see any desired aspect of the object. Sorealistic are the images produced by sophisticated CAD programs that itis difficult for the user not to believe that he is watching a realobject rather than just a computer simulation of a non-existent object.(Hereinafter for convenience, the term "real object" will be used todenote an object which physically exists in space-time, while the term"virtual object" will be used to denote a model which exists only as amathematical construct in a computer.)

Unfortunately, when the user of a CAD program wishes to produce a hardcopy of a three-dimensional virtual object, he finds that most availableforms of output are essentially two-dimensional. Typically, the userwill generate a hard copy of his results as a series of two-dimensionalsections through the object. While such a series of sections may beconvenient for preparing working drawings for manufacture of thecorresponding real object, such a series does not readily convey an ideaof the three-dimensional structure of the virtual object to mostobservers, particularly those not skilled in interpreting technicaldrawings.

Alternatively a series of images of the virtual object (showing, forexample, rotation of the object about one or more axes) may be recordedon video tape. However, not only is special equipment needed to convertcomputer data to conventional video standards, but the resultant videoimages are typically of low resolution, and restrict an observer of thetape to watching a series of two-dimensional views of the virtual objectchosen and fixed by the program's user, rather than allowing theobserver to choose his own selection and sequence of views of thevirtual object.

Holographic techniques can of course record full details of athree-dimensional virtual object and permit an observer to view thehologram as if it were a three-dimensional real object. However,holographic recording requires the use of a laser, and holograms of atype which can be viewed in white light display distracting colorchanges as the parallax of the hologram is observed.

Various techniques are known for recording three-dimensional images inlenticular media having one or more photosensitive layers. As early as1908, Gabriel Lippman invented a method for producing a truethree-dimensional image of a scene with vertical and horizontalparallax; see, for example, De Montebello, "Processing and Display ofThree-Dimensional Data II" in Proceedings of SPIE, San Diego, 1984. InLippman's method, a photographic plate is exposed through a "fly's eye"lens sheet, so that each lenslet forms a miniature image of the scenebeing reproduced, as seen from the perspective of the point on the sheetoccupied by that lenslet. After the photographic plate has beendeveloped, an observer looking at the composite image on the platethrough the lenticular sheet sees a three-dimensional representation ofthe scene photographed; this representation will be in color if a colorplate is used. If a lenticular sheet using hemicylindrical elongatelenticles is used instead of a fly's eye sheet, a similarthree-dimensional image is seen, but this image has parallax in only onedirection, across the length of the lenticles.

Unfortunately, because in Lippman's method the composite image has to beviewed from the same side of the lenticular screen as that on which thescene photographed originally stood, and because the image formed by thelenticles during exposure of the plate has undergone only a singleinversion of each miniature image, the three-dimensional representationproduced is pseudoscopic, that is to say the depth perception in theimage is inverted so that the object appears "inside out". To overcomethis problem, a number of variations of Lippman's method have beendevised to achieve two inversions of each miniature image in order toprovide an orthoscopic ("right side out") three-dimensional image; see,for example, U.S. Pat. No. 3,895,867. However, most of these variationsof Lippman's method are complex, involving multiple exposures with asingle camera, or multiple cameras or multi-lens cameras to record aplurality of views of the same object, and require extremely accurateregistration of multiple images to provide a single three-dimensionalimage. Moreover, any method for producing three-dimensional images whichrelies upon conventional cameras necessarily requires the presence of areal object before the camera, and such a method is ill-adapted forproducing three-dimensional images of a virtual object, since it ishighly undesirable to have to produce a real copy of the virtual objectmerely in order to effect the imaging process.

Thus, there is a need for a method of producing a three-dimensionalimage of an object which can readily be applied to imaging of virtualobjects without a need to first produce a real copy of the object.

SUMMARY OF THE INVENTION

This invention provides a method for the production of athree-dimensional image of an object, which method comprises:

(a) providing an imaging medium having on one surface thereof alenticular screen, the lenticles of the screen dividing the opposedsurface of the imaging medium into a plurality of elongate image areas,the imaging medium having on the opposed side thereof aradiation-sensitive layer, the radiation-sensitive layer comprising acolor-forming composition adapted to undergo a change of color uponincrease in the temperature of the radiation-sensitive layer above acolor-forming temperature for a color-forming time; and

(b) imagewise exposing the radiation-sensitive layer to actinicradiation which does not pass through the lenticular screen, therebycausing the color-forming composition to undergo its change in color inexposed areas and to form in the radiation-sensitive layer a compositeimage, the composite image comprising, in each of the image areas, aplurality of image strips extending lengthwise along the image area,each of the image strips containing information from a view of theobject, each of the plurality of image strips in one image areacontaining information from a different view of the object,

whereby a three-dimensional orthoscopic image of the object will appearto an observer seeing the composite image in the radiation-sensitivelayer through the lenticular screen.

(This method may hereinafter be referred to as the "three-dimensionalimaging method" of the present invention.)

This invention also provides an exposed imaging medium bearing athree-dimensional image, the imaging medium having on one surfacethereof a lenticular screen, and on the opposed surface thereof aradiation-sensitive layer having exposed and unexposed areas, theunexposed areas comprising a color-forming composition adapted toundergo a change of color upon increase in the temperature of theradiation-sensitive layer above a color-forming temperature for acolor-forming time, and the exposed areas comprising a colored materialresulting from exposure of the color-forming composition to heat, theexposed and unexposed areas being such that a three-dimensionalorthoscopic image of the object will appear to an observer seeing theimage in the radiation-sensitive layer through the lenticular screen.

This invention also provides an imaging medium having on one surfacethereof a lenticular screen, and on the opposed surface thereof aradiation-sensitive layer, the radiation-sensitive layer comprising acolor-forming composition adapted to undergo a change of color uponincrease in the temperature of the radiation-sensitive layer above acolor-forming temperature for a color-forming time.

Finally, this invention provides a method for printing an image on alenticular sheet in registration with the lenticles thereof, the imagecomprising a plurality of image areas each of which is to be printed inregister with a lenticle of the lenticular sheet, the method comprising:

providing, on the surface of the lenticular sheet remote from thelenticles, a radiation-sensitive layer, the radiation-sensitive layerbeing sensitive to radiation of a first wavelength but essentiallyinsensitive to radiation of a second wavelength;

passing a first beam of radiation of the second wavelength through thelenticular screen, and detecting the periodic variation of the radiationon the side of the imaging medium bearing the radiation-sensitive layer;

scanning a second beam of radiation of the first wavelength over theradiation-sensitive layer without passing the second beam through thelenticles of the lenticular sheet while modulating the intensity of thesecond beam, thereby imagewise exposing the radiation-sensitive layer toproduce the image, the modulation of the second beam being controlled independence upon the detected periodic variation so that each image areaof the image is formed in register with a lenticle of the lenticularsheet.

(This method may hereinafter be referred to as the "registration method"of the present invention.)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the accompanying drawings is a schematic cross section throughpart of an imaging medium of the present invention, and illustrates boththe three-dimensional imaging method and the registration method of thepresent invention;

FIG. 2 is an enlarged version of part of FIG. 1 showing details of theradiation-sensitive layer of the imaging medium; and

FIGS. 3 and 4 illustrate the manner in which a plurality of images of anobject may be produced and combined to effect the three-dimensionalimaging method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As already mentioned, the three-dimensional imaging method of thepresent invention uses an imaging medium having on one surface thereof alenticular screen; this screen is regarded as dividing the opposedsurface of the imaging medium into a plurality of elongate image areas.On the opposed side of the imaging medium is provided aradiation-sensitive layer comprising a color-forming composition adaptedto undergo a change of color upon increase in the temperature of theradiation-sensitive layer above a color-forming temperature for acolor-forming time. The radiation-sensitive layer is imagewise exposedto actinic radiation which does not pass through the lenticular screen,thereby causing the color-forming composition to undergo its change incolor in exposed areas and to form in the radiation-sensitive layer acomposite image. This composite image comprises, in each of the imageareas, a plurality of image strips extending lengthwise along the imagearea, each of the image strips containing information from a view of theobject, each of the plurality of image strips in one image areacontaining information from a different view of the object, such that anobserver seeing the composite image through the lenticular screen willsee a three-dimensional orthoscopic image of the object appearing behindthe imaging medium.

From the preceding paragraph, it will be seen that, in thethree-dimensional imaging method of the present invention, imagewiseexposure of the radiation-sensitive layer is effected with theradiation-sensitive layer affixed to the lenticular screen, so that thecomposite image is formed in situ on the imaging medium in alignmentwith the lenticles of the screen. Forming the image in this manner easesthe problem of accurately registering (aligning) the image formed on theradiation-sensitive layer with the lenticles of the screen; thisregistration problem causes great difficulty in certain prior artmethods for forming three-dimensional images, which prior art methodsrely upon first forming an image on a radiation sensitive mediumseparate from a lenticular screen, and then affixing the image to thescreen in registration with the lenticles thereon. Moreover, asdescribed in more detail below, the three-dimensional imaging andregistration methods of the present invention can be used simultaneouslyto achieve accurate registration of the image with the lenticles.

A variety of techniques known to persons skilled in the art ofthree-dimensional imaging may be used to determine the correct imagestrips to be included in the composite image written on theradiation-sensitive layer in the three-dimensional imaging method of thepresent invention. In one of the simpler techniques (described in moredetail below with reference to FIGS. 3 and 4, and also generallydescribed in Love et al., Computer Generated Lenticular Stereograms,SPIE, 1083, 102 (1989)), a plurality of two-dimensional images of theobject from various positions are determined (by optical methods or bycalculation), each of these two-dimensional images is separated into aplurality of strips equal in number to the number of lenticles behindwhich the composite image is to be written, and one strip from eachtwo-dimensional image (appropriately reduced in width to allow formaintenance of the correct aspect ratio of the object) is placed in eachof the image areas.

Other techniques which are useful for, or can be modified to be usefulfor, determination of the strips in the composite image are describedin, inter alia:

Valyus, N. A., Stereoscopy, Focal Press, London, pp. 195-207;

Davies et al., Three-dimensional imaging systems: a new development,Applied Optics, 27(21), 4520 (1988);

Li Yang et al., Discussion of the optics of a new 3-D imaging system,Applied Optics, 27(21), 4529 (1988);

Higuchi et al., Real-time transmission of 3-D images formed by parallaxpanoramagrams, Applied Optics, 17(24), 3895 (1978); and

C. W. Smith, New advances in 3D imagery, Brit. J. Photog., (1989), 14.

Although these various techniques differ in detail, most of them areequivalent to determining the images of a three-dimensional object lyingin front of a lenticular imaging medium which could be formed by eachlenticle on the image area lying immediately behind that lenticle (i.e.,determining the images actually formed in Lippman's method) and thenlaterally reversing the image thus formed in each image area across thelongitudinal center line of that image area (this lateral inversionensuring that the three-dimensional image seen by an observer lookingthrough the lenticles at the composite image is orthoscopic rather thanpseudoscopic).

Although, at least in theory, the determination of the image strips tobe included in the composite image used in the three-dimensional imagingmethod of the present invention could be carried out by purely opticalmethods (or by a combination of optical and mathematical methods, forexample forming a series of two-dimensional images of the object fromvarious positions by direct optical imaging of the object, scanning theresultant images to produce digital forms thereof, and combining theresultant digital images mathematically), the present invention isprimarily intended for producing three-dimensional images of virtualobjects produced by computer modelling or similar programs, and thus thedetermination of the image strips is desirably carried out bymathematical manipulation of the virtual object. Those skilled in theart of computer modelling are well aware of techniques for generatingthe necessary image strips; for example, if the image strips are to begenerated by combining parts of various views of a virtual object, asdescribed above, the various views are projections of the object on tovarious planes, and the ability to produce such projections is a routinefeature of CAD programs. Also, techniques for assembling the parts ofthe various views into the composite image are well within the abilityof those skilled in the art of image processing.

As in any three-dimensional imaging method which relies upon theformation of multiple image strips, the realism of the three-dimensionalimage produced by the present three-dimensional imaging method isaffected by the number of image strips in each image area, and it ispreferred that there be at least four image strips in each image area.To achieve more realistic parallax, it has been found desirable that theangular difference between adjacent views combined to produce thethree-dimensional image not exceed about 6°, and thus to enable a widerange of views of the object to be seen from the three-dimensionalimage, it is desirable to use more than four image strips, for example,ten to twenty image strips in each image area. However, increasing thenumber of image strips necessarily decreases the width of each imagestrip (which is equal to the spacing between adjacent lenticles dividedby the number of image strips) and hence reduces the number of pixelswhich can be accommodated within the width of a single image strip. Thisnumber of pixels affects the resolution of the image seen, and hence itmay be necessary to strike a balance between the number of image stripsin each image area (and hence the realism of the parallax of the image)and the resolution of the image. As noted below, it is one of theadvantages of the preferred color-forming compositions for use in thepresent three-dimensional imaging method that they are capable ofproducing very high resolution images, in excess of 3000 lines per inch(in excess of 120 lines/mm).

It should be noted that, in contrast to Lippman's method and opticalmodifications thereof, the angular range of views, which can be combinedinto the composite image used in the three-dimensional imaging method ofthe present invention (and which can thus be seen by an observer viewingthe three-dimensional image), is not limited by the "field of view" ofthe lenticles. In Lippman's method, only the portion of the image formedby each lenticle which falls within the image area of that lenticle iseffective in producing the three-dimensional image, since only theportion of the image formed by each lenticle which lies within theassociated imaging area is seen through that lenticle by the observer;portions of the image formed by each lenticle which lie outside theassociated imaging area effectively only produce "noise" in thethree-dimensional image. Thus, in Lippman's method, the angular spreadof images which contribute to the three-dimensional image is restrictedby the finite extent of the image area of each lenticle, and so is therange of view of the object which can be seen in the three-dimensionalimage produced. If the angular range of views included in an imageproduced by the three-dimensional imaging method of the presentinvention exceeds the range which could be included by Lippman's method,the parallax of the three-dimensional image will be false in that theobject will appear to move as the observer observes various viewsthereof, but the full angular range of views can still be seen by theobserver.

The images produced by the present method may be either monochromatic orpolychromatic. Polychromatic images are produced in a manner similar tothat employed in other polychromatic imaging media, namely by providinga radiation-sensitive layer comprising at least two radiation-sensitivesub-layers sensitive to radiation of differing wavelengths, and, in step(b), imagewise exposing the radiation-sensitive layer to actinicradiation of two differing wavelengths to form images in the tworadiation-sensitive sub-layers, so that a multicolored image is formedin the radiation-sensitive layer. Full color images may be achievedusing three sub-layers, which typically will form yellow, cyan andmagenta images, as in a conventional silver halide color film. Normally,the various radiation-sensitive sub-layers will be laid down one on topof the other within the radiation-sensitive layer, so that thesub-layers will be at differing distances from the lenticular sheet.Care should be taken to ensure that the sub-layers are not so thick thatthe realism of the three-dimensional image seen is affected by thisspacing between the sub-layers. The preferred color-forming compositionsfor use in the three-dimensional imaging method of the present inventioncan yield high optical densities of about 3.0 using radiation-sensitivelayers of the order of 1 μm thick.

Desirably, the imagewise exposure of the radiation-sensitive layer instep (b) is effected by scanning a beam of radiation (preferably a laserbeam) across the radiation-sensitive layer, and modulating the intensityof the beam to provide the imagewise variation in exposure. The use of alaser beam is not only well suited for recording in a scanning mode but,by utilizing a highly concentrated beam, exposure can be concentrated ina small area so that it is possible to record at high speed, highresolution and high density. Also, the use of a scanned laser beam is aconvenient way to record data in response to transmitted signals, suchas the digitized information form in which the image information willtypically be generated by the present method.

The three-dimensional imaging method of the present invention uses aradiation-sensitive layer comprise a color-forming composition adaptedto undergo a change of color upon increase in the temperature of theradiation-sensitive layer above a color-forming temperature for acolor-forming time. The preferred color-forming compositions describedbelow can be caused to undergo their color change with essentially nochange in dimensions of the radiation-sensitive layer. In contrast,conventional silver halide emulsions tend to shrink during development,and this shrinkage is highly disadvantageous in that it might affectregistration of the composite image with the lenticles. In addition, thepreferred color-forming compositions described below do not require anydevelopment steps, and thus avoid exposure of the lenticular screen todeveloping chemicals such as might occur if a silver halide materialwere used. Appropriate color-forming compositions for use in thethree-dimensional imaging method of the present invention are describedin, for example, U.S. Pat. Nos. 4,602,263; 4,720,449; 4,720,450;4,745,046; 4,826,976; and 4,960,901, the disclosures of which are hereinincorporated by reference.

Preferred color-forming compositions for use in the presentthree-dimensional imaging method are:

a. an organic compound capable of undergoing, upon heating, anirreversible unimolecular fragmentation of at least one thermallyunstable carbamate moiety, this organic compound initially absorbingradiation in the visible or the non-visible region of theelectromagnetic spectrum, said unimolecular fragmentation visiblychanging the appearance of the organic compound (see U.S. Pat. No.4,602,263);

b. a substantially colorless di- or triarylmethane imaging compoundpossessing within its di- or triarylmethane structure an aryl groupsubstituted in the ortho position to the meso carbon atom with a moietyring-closed on the meso carbon atom to form a 5- or 6-membered ring,said moiety possessing a nitrogen atom bonded directly to said mesocarbon atom and said nitrogen atom being bound to a group with a maskedacyl substituent that undergoes fragmentation upon heating to liberatethe acyl group for effecting intramolecular acylation of said nitrogenatom to form a new group in the ortho position that cannot bond to themeso carbon atom, whereby said di- or triarylmethane compound isrendered colored (see U.S. Pat. No. 4,720,449);

c. a colored di- or triarylmethane imaging compound possessing withinits di- or triarylmethane structure an aryl group substituted in theortho position to the meso carbon atom with a thermally unstable ureamoiety, said urea moiety undergoing a unimolecular fragmentationreaction upon heating to provide a new group in said ortho position thatbonds to said meso carbon atom to form a ring having 5 or 6 members,whereby said di- or triarylmethane compound becomes ring-closed andrendered colorless (see U.S. Pat. No. 4,720,450);

d. in combination, a substantially colorless di- or triarylmethanecompound possessing on the meso carbon atom within its di- ortriarylmethane structure an aryl group substituted in the ortho positionwith a nucleophilic moiety which is ring-closed on the meso carbon atom,and an electrophilic reagent which upon heating and contacting said di-or triarylmethane compound undergoes a bimolecular nucleophilicsubstitution reaction with said nucleophilic moiety to form a colored,ring-opened di- or triarylmethane compound (see U.S. Pat. No.4,745,046);

e. a compound of the formula ##STR2## wherein M' has the formula:##STR3## wherein R is alkyl; --SO₂ R¹ is alkyl; phenyl; naphthyl; orphenyl substituted with alkyl, alkoxy, halo, trifluoromethyl, cyano,nitro, carboxy, --CONR² R³ wherein R² and R³ each are hydrogen or alkyl,--CO₂ R⁴ wherein R⁴ is alkyl or phenyl, --COR⁵ wherein R⁵ is amino,alkyl or phenyl, --NR⁶ R⁷ wherein R⁶ and R⁷ each are hydrogen or alkyl,--SO₂ NR⁸ R⁹ wherein R⁸ and R⁹ each are hydrogen, alkyl or benzyl; Z'has the formula: ##STR4## wherein R' is halomethyl or alkyl; X is --N═,--SO₂ -- or --CH₂ --; D taken with X and M' represents the radical of acolor-shifted organic dye; q is 0 or 1; and p is a whole number of atleast 1; said Z' being removed from said M' upon the application of heatto effect a visually discernible change in spectral absorptioncharacteristics of said dye (see U.S. Pat. No. 4,826,976);

f. a substantially colorless di- or triarylmethane compound of theformula: ##STR5## wherein ring B represents a carbocyclic aryl ring or aheterocyclic aryl ring; C₁ represents the meso carbon atom of said di-or triarylmethane compound; X represents --C(═O)--; --SO₂ -- or --CH₂ --and completes a moiety ring-closed on said meso carbon atom, said moietyincluding the nitrogen atom bonded directly to said meso carbon atom; Yrepresents --NH--C(═O)--L, wherein L is a leaving group that departsupon thermal fragmentation to unmask --N═C═O for effectingintramolecular acylation of said nitrogen atom to open the N-containingring and form a new group in the ortho position of ring B that cannotbond to said meso carbon atom; E is hydrogen, an electron-donatinggroup, an electron-withdrawing group or a group, either anelectron-donating group or an electron-neutral group that undergoesfragmentation upon heating to liberate an electron-withdrawing group; sis 0 or 1; and Z and Z' taken individually represent the moieties tocomplete the auxochromic system of a diarylmethane or triarylmethane dyewhen said N-containing ring is open, and Z and Z' taken togetherrepresent the bridged moieties to complete the auxochromic system of abridged triarylmethane dye when said N-containing ring is open (see U.S.Pat. No. 4,960,901);

g. a colorless precursor of a preformed image dye substituted with (a)at least one thermally removable protecting group that undergoesfragmentation from said precursor upon heating and (b) at least oneleaving group that is irreversibly eliminated from said precursor uponheating, provided that neither said protecting group nor said leavinggroup is hydrogen, said protecting and leaving groups maintaining saidprecursor in its colorless form until heat is applied to effect removalof said protecting and leaving groups whereby said colorless precursoris converted to an image dye (see International Patent Application No.PCT/US89/02965 (Publication No. WO 90/00978), U.S. Pat. No. 5,192,645,and copending application Ser. No. 07/729,426, filed Jul. 12, 1991;

h. a mixed carbonate ester of a quinophthalone dye and a tertiaryalkanol containing not more than about 9 carbon atoms (see U.S. Pat. No.5,243,052)

i. a leuco dye represented by: ##STR6## wherein:

E represents a thermally removable leaving group;

tM represents a thermally migratable acyl group;

Q, Q' and C taken together represent a dye-forming coupler moietywherein C is the coupling carbon of said coupler moiety;

and, (Y) taken together with N represents an aromatic amino colordeveloper,

one of said Q, Q' and (Y) containing an atom selected from the atomscomprising Group 5A/Group 6A of the Periodic Table, said groups E and tMmaintaining said leuco dye in a substantially colorless form until theapplication of heat causes said group E to be eliminated from said leucodye and said group tM to migrate from said N atom to said Group 5A/Group6A atom thereby forming a dye represented by: ##STR7## wherein saiddotted lines indicate that said tM group is bonded to said Group5A/Group 6A atom in one of said Q, Q' and (Y) (see U.S. Pat. No.5,236,884).

These preferred color-forming compositions rely on a chemical reactionwith a substantial activation energy to form a covalent bond for colorformation, rather than upon a diffusion-controlled reaction, for examplebetween an electron-donating compound (color former) and anelectron-accepting compound (color developer). Thus, these preferredcolor-forming compositions can be in the form of a single phasecomposition which is essentially stable at room temperature but whichforms color when heated above its color-forming temperature for acolor-forming time, in contrast to certain thermal imaging systems whichcontain two separate phases, each of which contains one component of atwo-component color-forming system, such that admixing of the two phaseswill result in color formation at any temperature, these two phasesbeing arranged not to diffuse into one another at room temperature butto diffuse into one when the two phase system, as for example by ruptureof the walls of microcapsules in which one of the phases isencapsulated.

As described in the patents mentioned above, these preferredcolor-forming compositions are capable of producing very high resolutionimages which require no development, and thus these color-formingcompositions are well-suited to imaging in situ in the method of thepresent invention. Furthermore, as already mentioned the imaging processproduces essentially no change in the dimensions of the color-formingcomposition, thus avoiding any problems in maintaining registration ofthe three-dimensional image with the lenticular screen.

As already mentioned, the imagewise exposure step of the present methodis conveniently effected using a laser. In the present state oftechnology, solid state diode infra-red lasers emitting at about 700 to1200 nm, preferably 800 to 1200 nm, provide the highest output per unitcost, and thus are desirably used in the present process, especiallysince the output from such solid state diodes can be shaped by opticalmethods into a elongate spot only about 3-5 μm in its short dimension byabout 20 μm in its long dimension, and such an elongate spot iswell-suited for use in the present method. (Because of the elongatelenticles and elongate image strips used in the present method,resolution across the image strips is much more important thanresolution along the strips, and resolution across the strips can bemaximized by orienting the elongate laser spot with its short dimensiondisposed across the image strips and its long dimension along the imagestrips.)

Since most of the preferred color-forming compounds do not absorbstrongly in the infra-red, in the imaging medium of the presentinvention the radiation-sensitive layer desirably comprises an absorbercapable of absorbing infra-red radiation and thereby generating heat inthe radiation-sensitive layer. The heat thus generated is transferred tothe color-forming compound to initiate the color-forming reaction andeffect the change in the absorption characteristics of the color-formingcompound from colorless to colored. Obviously, the infra-red absorber(which may also be referred to hereinafter as an "infra-red dye") shouldbe in heat-conductive relationship with the color-forming compound, forexample, in the same layer as the color-forming compound or in anadjacent layer. Though an inorganic compound may be employed, theinfra-red absorber preferably is an organic compound, such as a cyanine,merocyanine, squarylium, thiopyrylium or benzpyrylium dye, andpreferably, is substantially non-absorbing in the visible region of theelectromagnetic spectrum so that it will not contribute any substantialamount of color to the D_(min) areas, i.e., the highlight areas of theimage. The light absorbed by the respective infra-red absorbers isconverted into heat and the heat initiates the reaction to effect theformation of colored compounds in the color-forming layers. Since thistype of radiation-sensitive layer is imaged by infra-red radiationrather than by direct heating, a high resolution image is more easilyachieved.

An especially preferred form of radiation-sensitive layer of this typehas at least two sub-layers, the at least two sub-layers comprisingcolor-forming compounds arranged to produce dye compounds havingdiffering colors, and comprising absorbers absorbing at differingwavelengths. The infra-red absorbers are desirably selected such thatthey absorb radiation at different predetermined wavelengths above 700nm sufficiently separated so that each color-forming layer may beexposed separately and independently of the others by using infra-redradiation at the particular wavelengths selectively absorbed by therespective infra-red absorbers. As an illustration, three color-formingsub-layers containing yellow, magenta and cyan color-forming compoundscould have infra-red absorbers associated therewith that absorbradiation at 792 nm, 848 nm and 926 nm, respectively, and could beaddressed by laser sources, for example, infra-red laser diodes,emitting laser beams at these respective wavelengths so that the threecolor-forming sub-layers can be exposed independently of one another.While each sub-layer may be exposed in a separate scan, it is usuallypreferred to expose all of the color-forming sub-layers in a single scanusing multiple laser sources of the appropriate wavelengths. In suchmulti-color radiation-sensitive layers, the color-forming compounds maycomprise the subtractive primaries yellow, magenta and cyan or othercombinations of colors, which combinations may additionally includeblack. The leuco dyes generally are selected to give the subtractivecolors cyan, magenta and yellow, as commonly employed in photographicprocesses to provide full natural color. A full color imaging medium ofthis type having three color-forming sub-layers is described below withreference to FIG. 2 of the accompanying drawings.

Where imagewise heating is induced by converting light to heat, theradiation-sensitive layer may be heated prior to or during exposure.This may be achieved using a heating platen or heated drum or byemploying an additional laser source or other appropriate means forheating the radiation-sensitive layer while it is being exposed.

The preferred color-forming compositions described above are essentiallyinsensitive to visible light. This insensitivity to visible light notonly allows imaging media of the present invention comprising thepreferred color compositions to be handled freely under normal roomlighting, but also facilitates registration of the image with thelenticular screen using the registration method of the presentinvention. In this registration method, as already mentioned, to achieveregistration of the image with the lenticular screen a beam ofnon-imaging radiation, of a wavelength which does not image theradiation-sensitive layer, is passed through the lenticular screen, andthe periodic variation of the non-imaging radiation on the side of theimaging medium bearing the radiation-sensitive layer is used to controlthe registration of the composite image with the lenticles of thescreen. Those skilled in the electronic imaging art are well aware oftechniques which can be used to control the registration of thecomposite image with the lenticular screen depending upon the periodicvariation of the non-imaging radiation which has passed through thescreen. For example, a linear solid state imager could be placed on theside of the imaging medium bearing the radiation-sensitive layer withits long dimension extending across the lenticles, and the periodicvariation of the non-imaging radiation detected by the solid stateimager used to control timing circuits which control the modulation ofthe imaging laser beam. When using a near infra-red laser for imaging aradiation-sensitive layer which is essential unaffected by visibleradiation, the non-imaging radiation can be visible light.

The imaging medium of the present invention can be prepared in a mannersimilar to the thermal imaging media described in the aforementionedU.S. patents and applications. Typically, as described in these U.S.patents, the color-forming compound and any other components of thecolor-forming layer (for example, a polymeric binder and an infra-redabsorber) are dispersed in an appropriate solvent, and the resultantliquid dispersion is coated onto a support, generally a polymer film,using conventional coating equipment, and the resultant liquid filmdried to produce the color-forming layer. To produce an imaging mediumof the present invention, the coating operation may be carried out usinga lenticular sheet in place of a simple polymeric film, appropriateprecautions (for example, the use of rubber-coated rollers) being usedif necessary to ensure that the lenticular surface of the sheet is notdamaged or deformed during the coating operation. Alternatively, theradiation-sensitive layers can be coated onto a conventional support,and the resultant combination of support and radiation-sensitive layerslaminated to the lenticular medium under heat and pressure or by the useof adhesives. If a relatively thick support is desired for ease ofcoating but the presence of such a thick support is deemed undesirableduring imaging (because, for example, inevitable manufacturingvariations in a thick support may make it difficult to control the depthof focus of a laser imaging micrometer thick radiation-sensitivelayers), the support may comprise a strip sheet which is peeled from theradiation-sensitive layers after those layers have been laminated to thelenticular medium. Appropriate strip sheets are well-known to thoseskilled in the coating art; for example, the types of strip sheets usedto support thin metal layers in hot strip foils may be used to supportthe radiation-sensitive layers. The coating operation can be carried outusing conventional machinery such that the lenticular surface is notexposed to the coating composition.

Rather than a solution coating, the radiation-sensitive layer may beapplied as a dispersion or an emulsion. The coating composition also maycontain dispersing agents, plasticizers, defoaming agents, hinderedamine light stabilizers and coating aids. In forming theradiation-sensitive layer, temperatures should be maintained belowlevels that will cause the color-forming reactions to occur rapidly sothat the color-forming compounds will not be prematurely colored.

The imaging medium of the present invention may contain additionallayers and components as described in the aforementioned U.S. patentsand applications. The lenticular sheet should be sufficiently thick asto permit easy handling of the imaging medium, and may be any materialthat substantially retains its dimensional stability during imaging andhas a refractive index sufficient to provide adequate reconstruction ofthe three-dimensional image. Desirably, the lenticular sheet has athickness of at least about 50 μm. The lenticular sheet must besufficiently transparent that it does not raise excessively the D_(min)of the final image. Suitable sheets may be formed from, for example,polyethylene, polypropylene, polycarbonate, cellulose acetate, andpolystyrene.

Examples of binders that may be used in the radiation-sensitive layerinclude poly(vinyl alcohol), poly(vinyl pyrrolidone), methyl cellulose,cellulose acetate butyrate, styrene-acrylonitrile copolymers, copolymersof styrene and butadiene, poly(methyl methacrylate), copolymers ofmethyl and ethyl acrylate, poly(vinyl acetate), poly(vinyl butyral),polyurethane, polycarbonate and poly(vinyl chloride). It will beappreciated that the binder selected should not have any adverse effecton the leuco dye incorporated therein and may be selected to have abeneficial effect. Also, the binder should be substantially heat-stableat the temperatures encountered during image formation and it should betransparent so that it does not interfere with viewing of the colorimage. Where electromagnetic radiation is employed to induce imagewiseheating, the binder also should transmit the radiation intended toinitiate image formation.

As explained in more detail in the aforementioned copending U.S.application Ser. No. 07/696,196, in some imaging media of the typedescribed in the aforementioned patents, there is a tendency for one ormore of the colored materials produced during imaging to diffuse out oftheir color-forming layers, but such undesirable diffusion of coloredmaterial can be reduced or eliminated by dispersing the leuco dye in afirst polymer having a glass transition temperature of at least about50° C., preferably at least about 75° C., and most preferably at leastabout 95° C. and providing a diffusion-reducing layer in contact withthe color-forming layer, this diffusion-reducing layer comprising asecond polymer having a glass transition temperature of at least about50° C. and being essentially free from the color-forming composition.Desirably, the diffusion-reducing layer has a thickness of at leastabout 1 μm. The first polymer is desirably an acrylic polymer,preferably poly(methyl methacrylate).

As discussed in the aforementioned U.S. application Ser. No. 07/695,641,certain color-forming compounds show a tendency to form bubbles duringimaging. Accordingly, the imaging medium of the present inventionadvantageously comprises a bubble-suppressant layer on the side of theradiation-sensitive layer remote from the lenticular sheet and having athickness of at least about 10 μm, such that, upon imagewise increase inthe temperature of the radiation-sensitive layer above the color-formingtemperature for the color-forming time, in heated regions theradiation-sensitive layer undergoes its change of color but remainsessentially free from bubbles.

Other layers which may be included in the imaging medium of the presentinvention are, for example, a subbing layer to improve adhesion of theradiation-sensitive layer to the lenticular sheet, interlayers forthermally insulating multiple color-forming sub-layers from each other,an ultra-violet screening layer having an ultraviolet absorber therein,or other auxiliary layers. To give good protection against ultra-violetradiation, ultra-violet screening layers are desirably provided on bothsides of the radiation-sensitive layer; conveniently, one of theultra-violet screening layers is provided by using as the lenticularsheet a polymer film containing an ultra-violet absorber.

A preferred embodiment of the invention will now be described, though byway of illustration only, with reference to the accompanying drawings.These drawings are not to scale; in particular, the thicknesses of thevarious sub-layers of the radiation-sensitive layer are greatlyexaggerated in FIG. 2 relative to the size of the lenticles showntherein, while in FIG. 1 the size of the lenticles are exaggeratedrelative to the distance between the imaging medium and the "object"being imaged.

FIG. 1 shows an imaging medium (generally designated 10) comprising arectangular lenticular sheet 12 formed of a polymeric material andhaving on its upper surface (as illustrated in FIG. 1) a lenticularscreen 14 formed of a plurality of parallel, hemicylindrical lenticles16a, 16b etc., which run parallel to one edge of the sheet, andperpendicular to the plane of FIG. 1. On the lower surface of thelenticular sheet 12 is provided a radiation-sensitive layer 18.

The imaging medium 10 is shown in FIG. 1 disposed adjacent an "object"20. As explained above, the present method will normally be used toimage a virtual object, not a real one, so that in practice no realobject will be present adjacent the imaging medium 10 during imaging,but for purposes of explaining the invention it is convenient to discussthe method as though a real object were present on the lenticular screenside of the imaging medium. The object 20 is accordingly shown in FIG. 1in broken lines to indicate that it is only a hypothetical object.

FIG. 1 shows the imaging medium 10 as it is being imaged by threeinfra-red laser beams hν₁, hν₂ and hν₃, which are provided by a lasersource, schematically indicated at 22, the laser beams being directed onto the radiation-sensitive layer from below the imaging medium 10 sothat they do not pass through the lenticular screen 14. Simultaneously,a beam V of collimated visible radiation is directed on to thelenticular screen 14 perpendicular to the plane of the imaging medium10. The individual lenticles 16a, 16b etc. focus the beam V, therebyproducing, adjacent the lower surface of the imaging medium 10, a region24 in which the intensity of the visible radiation varies periodicallyin intensity across the imaging medium 10 with a period equal to thespacing between adjacent lenticles 16a, 16b etc. A linear solid stateimager 26 is movable within the region 24 so as to detect the periodicvariation in intensity of the visible radiation within this region.

The structure of the radiation-sensitive layer 18 is shown in moredetail in FIG. 2. As shown in that Figure, immediately adjacent thelenticular sheet 12 is a diffusion-reducing subcoat 28 approximately 1μm thick formed from a 10:1 w/w mixture of a water-dispersible styreneacrylic polymer (Joncryl 538 sold by S. C. Johnson & Son, Inc., RacineWis. 53403) and a water-soluble acrylic polymer (Carboset 526 sold byThe B. F. Goodrich Co., Akron Ohio 44313). The presence of the minorproportion of water-soluble acrylic polymer reduces the tendency for thelayer 28 to crack during the coating process. The diffusion-reducingsubcoat 28, which has a glass transition temperature of approximately55° C., serves the function of a conventional subcoat, namely increasingthe adhesion of the imaging layer 30 (described in detail below) to thelenticular sheet 12. The subcoat 28 also serves to reduce or eliminatemigration of dye compound from the imaging layer 30 after imaging; if aconventional subcoat were employed in place of the diffusion-reducingsubcoat 28, diffusion of the dye compound from the layer 30 into thesubcoat after imaging might cause loss of quality of the image. Thesubcoat 28 is coated onto the lenticular sheet 12 from an aqueous mediumcontaining the water-dispersible and water-soluble polymers.

A yellow imaging layer 30 is in contact with the diffusion-reducingsubcoat 28. This imaging layer 30 is approximately 5 μm thick andcomprises approximately 47.5 parts by weight of a leuco dye of theformula: ##STR8## in which R' is a tertiary butyl group (the compoundsin which R' is an isobutyl or benzyl group may alternatively be used),1.6 parts by weight of an infra-red dye of the formula: ##STR9##(prepared as described in copending U.S. application Ser. No.07/795,038, filed Nov. 20, 1991, and the corresponding InternationalApplication No. PCT/US91/08695; essentially, this dye is produced bycondensing two moles of a2-(1,1-dimethylethyl)-5,7-dimethoxy-4-methylbenzpyrylium salt with acroconate salt), 3.3 parts by weight of a hindered amine stabilizer(HALS-63, sold by Fairmount Chemical Co.), and 47.5 parts by weight of apoly(methyl methacrylate) binder (Elvacite 2021, sold by DuPont deNemours, Wilmington, Del.; this material is stated by the manufacturerto be a methyl methacrylate/ethyl acrylate copolymer, but its glasstransition temperature approximates that of poly(methyl methacrylate)).This binder has a glass transition temperature of approximately 110° C.The imaging layer 30 is applied by coating from a mixture of heptanesand methyl ethyl ketone.

Superposed on the yellow imaging layer 30 is a diffusion-reducing layer32, which, like the first diffusion-reducing layer 28, serves to preventmigration of dye compound from the yellow imaging layer 30 on storageafter imaging. The diffusion-reducing layer 32, which is approximately 2μm thick, is formed of a water-dispersible styrene acrylic polymer(Joncryl 138 sold by S. C. Johnson & Son, Inc., Racine Wis. 53403), andis coated from an aqueous dispersion. This layer has a glass transitiontemperature of approximately 60° C.

The next component of the radiation-sensitive layer 18 is asolvent-resistant interlayer 34 approximately 4.6 μm thick and composedof a major proportion of partially cross-linked polyurethane (NeoRezXR-9637 polyurethane sold by ICI Resins US, Wilmington, Mass.) and aminor proportion of poly(vinyl alcohol) (Airvol 540, sold by AirProducts and Chemicals, Inc., Allentown Pa. 18195). Thissolvent-resistant interlayer 34 is coated from an aqueous dispersion.The interlayer 34 not only helps to thermally insulate the imaginglayers 28 and 36 (described below) from one another during imaging, butalso prevents disruption and/or damage to the yellow imaging layer 30and the diffusion-reducing layer 32 during coating of the magentaimaging layer 36. Since the yellow imaging layer 30 and the magentaimaging layer 36 are both coated from organic solution, if asolvent-resistant interlayer were not provided on the layer 30 beforethe layer 36 was coated, the organic solvent used to coat the layer 36might disrupt, damage or extract leuco dye or infra-red absorber fromthe layer 30. Provision of the solvent-resistant interlayer 34, which isnot dissolved by and does not swell in the organic solvent used to coatthe layer 36, serves to prevent disruption of or damage to the layer 30as the layer 36 is coated. Furthermore, the solvent-resistant interlayer34 serves to prevent the magenta leuco dye, infra-red dye and hinderedamine light stabilizer from the layer 36 sinking into thediffusion-reducing layer 32 and the yellow imaging layer 30 as the layer36 is being coated.

Superposed on the solvent-resistant interlayer 34 is the magenta imaginglayer 36, which is approximately 3 μm thick and comprises approximately47.25 parts by weight of a leuco dye of the formula: ##STR10## (thisleuco dye may be prepared by the methods described in U.S. Pat. Nos.4,720,449 and 4,960,901), approximately 3.4 parts by weight of zincacetate (thus giving a leuco dye: zinc cation molar ratio of about1:0.4), 1.62 parts by weight of an infra-red dye of the formula:##STR11## (which may be prepared by the process described in U.S. Pat.No. 5,227,498; essentially, this dye is produced by reacting a compoundof the formula: ##STR12## in which R is a halogen atom or an alkylgroup, with diethylamine to introduce the -NEt₂ group on the squaryliumring, and then reacting the product with the 4-methylbenzpyrylium saltto give the final infra-red dye of Formula IR2), 3.6 parts by weight ofa hindered amine stabilizer (HALS-63), 0.27 parts by weight of a wettingagent, and 47.25 parts by weight of a polyurethane binder (Estane 5715,supplied by The B. F. Goodrich Co., Akron Ohio 44313). The imaging layer36 is applied by coating from a cyclohexanone/methyl ethyl ketonemixture.

(Alternatively, the infra-red dye of Formula IR2 above may be replacedby the dye of formula: ##STR13## (used in the form of itstetrafluoroborate salt) (this infra-red dye may be prepared by theprocess analogous to that used to prepare the infra-red dye of FormulaIR2 above using the corresponding selenopyrylium squaric acid derivativeand ammonia to introduce the amino group, followed by condensation ofthe product with a selenopyrylium salt; to prepare the selenopyryliumsquaric acid derivative, the corresponding selenopyrylium salt issubstituted for the benzpyrylium salt).)

On the imaging layer 36 is coated a second solvent-resistant interlayer38 which is formed from the same material, and coated-in the same manneras, the solvent-resistant interlayer 34.

Superposed on the second solvent-resistant interlayer 38 is a cyanimaging layer 40, which is approximately 3 μm thick and comprisesapproximately 49.5 parts by weight of a leuco dye of the formula:##STR14## (this leuco dye may by prepared by the methods described inthe aforementioned U.S. Pat. Nos. 4,720,449 and 4,960,901),approximately 3.97 grams of zinc acetate (thus giving a leuco dye: zinccation molar ratio of about 1:0.4), 1.62 parts by weight of an infra-reddye of the formula: ##STR15## (which is preferably prepared by theprocess described in copending U.S. Pat. No. 5,231,190; essentially thisprocess comprises reacting a diester, diacid chloride or monoestermonoacid chloride of squaric acid with a2-(1,1-dimethylethyl)7-diethylamino-4-methylbenzpyrylium salt andhydrolysing to produce a benzpyrylium-methylidene compound, and thenreacting this compound with a7-alkoxy-2-(1,1-dimethylethyl)-4-methylbenzpyrylium salt to give thefinal infra-red dye), 0.2 parts of a wetting agent, and 49.5 parts byweight of a polyurethane binder (Estane 5715). The imaging layer 40 isapplied by coating from methyl ethyl ketone.

(Alternatively, the infra-red dye of Formula IR4 above may be replacedby the dye of formula: ##STR16## (which may be prepared by a processanalogous to that used to prepare the infra-red dye of Formula IR2above, by reacting the intermediate of Formula V above with ammonia tointroduce an amino group on the squarylium ring, then reacting theproduct with a 4-methylbenzpyrylium salt to produce the amino squaryliumdye, and finally reacting this amino squarylium dye with pivaloylchloride to produce the final pivaloylamino group on the squaryliumring).

As already indicated, the layers 28-40 of the radiation-sensitive layer18 may be produced by coating on to the lenticular sheet 12. However,the remaining layers of the radiation-sensitive layer 18, namely atransparent bubble-suppressant layer 46, an ultraviolet filter layer 44and an adhesive layer 42 are not coated on to the lenticular sheet 12but rather are prepared as a separate unit and then laminated to theremaining layers of the radiation-sensitive layer 18.

The transparent bubble-suppressant layer 46 is a 1.75 mil (44 μm) PETfilm, a preferred film being that sold as ICI 505 film by ICI Americas,Inc., Wilmington, Del. The bubble-suppressant layer 46 prevents theformation of bubbles in the imaging layers 30, 36 and 40 of theradiation-sensitive layer 18 during imaging.

The ultraviolet filter layer 44 serves to protect the imaging layers 30,36 and 40 from the effects of ambient ultraviolet radiation. It has beenfound that the leuco dyes are susceptible to undergoing color changeswhen exposed to ultraviolet radiation during storage before or afterimaging; such color changes are obviously undesirable since theyincrease the D_(min) of the image and may distort the colors therein.The ultraviolet filter layer 44 is approximately 5 μm thick andcomprises approximately 83 percent by weight of a poly(methylmethacrylate) (Elvacite 2043, sold by DuPont de Nemours, Wilmington,Mass.), 16.6 percent by weight of an ultraviolet filter (Tinuvin 328sold by Ciba-Geigy, Ardsdale N.Y.) and 0.4 percent by weight of awetting agent. The ultraviolet filter layer 44 is prepared by coating onto the bubble-suppressant layer 46 from a solution in methyl ethylketone.

The adhesive layer 42, which is approximately 2 μm thick, is formed of awater-dispersible styrene acrylic polymer (Joncryl 138 sold by S. C.Johnson & Son, Inc., Racine Wis. 53403) and is coated on to theultraviolet filter layer 44 from an aqueous dispersion.

After the layers 44 and 42 have been coated on to the bubble-suppressantlayer 46, the entire structure containing these three layers islaminated under heat (approximately 225° F,. 107° C.) and pressure tothe structure containing the layers 12 and 28-40 to form the completeimaging medium 10.

If desired, the bubble-suppressant layer 46 may be formed by coating,rather than by lamination of a pre-formed film on to the layers 28-40.If the bubble-suppressant layer 46 is to be formed by coating, it isconvenient to incorporate an ultra-violet absorber into thebubble-suppressant layer, thereby avoiding the need for a separateultra-violet absorber layer. Thus, in this case, the layer 42 is coatedon to the layer 40 using the solvent already described, and then thebubble-suppressant layer 46 containing the ultra-violet absorber may becoated on to the layer 42 from an aqueous medium.

Alternatively, all the layers 28-44 of the imaging medium could becoated on to the bubble-suppressant layer 46, and the resultantstructure laminated under heat and pressure to the lenticular sheet 12.In view of the small thickness of the layer 46, the necessary coatingoperations may be carried out more easily if the layer 46 is firstlaminated to a suitable strip sheet (say 3 mil (77 μm) thick), and thisstrip sheet removed from the layer 46 after all the layers 28-46 havebeen laminated to the lenticular sheet 12.

The medium 10 is imaged by exposing it to the aforementioned beams hν₁,hν₂ and hν₃ (see FIG. 1) from three infra-red lasers having wavelengthsof approximately 792, 848 and 926 nm respectively. The 926 nm beamimages the yellow imaging layer 30, the 848 nm beam images the magentaimaging layer 36 and the 792 nm beam images the cyan imaging layer 40.Thus, a multicolor image is formed in the radiation-sensitive layer 18,and this multicolor image requires no further development steps.Furthermore, the medium 10 may be handled in normal room lighting priorto exposure, and the apparatus in which the imaging is performed neednot be light-tight. As already mentioned, modulation of the laser beamshν₁, hν₂ and hν₃ is controlled by timing circuits which receive theoutput of the solid state imager 26 so that the image written on theradiation-sensitive layer 18 by the beams hν₁, hν₂ and hν₃ is accuratelyregistered with the lenticles 16a, 16b etc.

The steps of the method of the present invention are illustrated inFIGS. 3 and 4. For ease of illustration, the present method isillustrated in FIGS. 3 and 4 using only four image strips per imagearea, although in practice it is desirable to use a greater number ofimage strips per image area to achieve greater realism in thethree-dimensional image seen by the observer. In addition, although FIG.4 shows the method being applied to a lenticular sheet containing onlyfive lenticles, in practice far more lenticles, typically from 100-300or more, will be present in the lenticular sheet. Finally, for ease ofexplanation, FIG. 3 illustrates the invention as applied to a realobject, although as explained above the present three-dimensionalimaging method will normally be applied to a virtual object, so that thevarious views of the object shown in FIG. 3 will normally be generatedby mathematical manipulation of a virtual object rather than byobtaining an image of a real object. However, it will be apparent tothose skilled in the art that there is no essential difference betweenapplying the present methods to images obtained by viewing a real objectand applying the same methods to images derived by mathematicalmanipulation of a virtual object.

FIG. 3 shows a camera 50 with an imaging medium lying in the same plane52 relative to the object 20 as the radiation-sensitive layer 18occupies in FIG. 1. The camera 50 is placed at four differing positionsin the plane 52, and images 54A, 54B, 54C and 54D are obtained, withimage 54A being taken from the leftmost position relative to the object20 and image 54D being taken from the rightmost position relative to theobject. Each of these images 54A, 54B, 54C and 54D are obtained aredivided into a number of strips equal to the number of image areas inwhich the composite image is to be formed (five in FIGS. 3 and 4), theimage strips being designated A1-A5, B1-B5, C1-C5 and D1-D5respectively, each series of image strips being numbered from left toright in FIG. 3.

As shown in FIG. 4, a composite image is formed in theradiation-sensitive layer 18 by assembling the image strips in aparticular order. The composite image is to be viewed through thelenticular screen 14 by an observer having left and right eyes L and Rrespectively. Behind the righthandmost lenticle 60 (as seen by theobserver) are assembled strips A1, B1, C1 and D1, these strips beingassembled in order from right to left from the observer's viewingdirection. Similarly, strips A2, B2, C2 and D2 are assembled behind thenext lenticle 62, and similar arrangements of strips are effected behindlenticles 64, 66 and 68, with the lefthandmost lenticle 68 as seen bythe observer receiving strips A5, B5, C5 and D5 from the righthand edgesof the images 54A, 54B, 54C and 54D respectively.

The composite image thus assembled is written into theradiation-sensitive layer 18 in the manner already described. Theobserver, seeing this composite image through the lenticular screen 12,will observe an orthoscopic three-dimensional image 20' appearing thesame distance behind the plane of the radiation-sensitive layer 18 asthe original object 20 lay in front of the plane 52 from which theimages 54A, 54B, 54C and 54D were taken.

It will be apparent to those skilled in the imaging art that, if theorthoscopic image thus produced is to retain the correct aspect ratio ofthe object 20, the widths of the strips present in the composite imagemust be reduced by a factor of four from the widths of the strips A1-A5,B1-B5, C1-C5 and D1-D5, since the composite image is twenty strips wide,whereas the original images 54A, 54B, 54C and 54D are each only fivestrips wide. The necessary reduction is width of the strips in thecomposite image could if desired by effected optically (for example byforming the images 54A, 54B, 54C and 54D using an anamorphic lens), butis more conveniently effected by digital image manipulation, especiallywhen the "images" themselves are created from a virtual object. In adigital image, each of the strips A1-A5, B1-B5, C1-C5 and D1-D5 willcomprise a plurality of columns of pixels, and the necessary widthreduction can be achieved simply by reducing the number of columns ineach strip, for example either by discarding three out of each group offour adjacent columns, or by averaging the four pixels in each row ofeach group of four adjacent columns, thereby producing a single columnof pixels which is an average of the original four adjacent columns.

It will readily be apparent to those skilled in the imaging art thatnumerous changes and modifications may be made to the specificembodiment of the invention described above without departing the scopeof the invention. For example, instead of using hemicylindricallenticles, lenticles having forms derived from non-spherical surfacescould be used. In addition, numerous changes can be made during theproduction of the image before it is written on to theradiation-sensitive layer. For example, the object could be distorted byexpanding it in one dimension and/or contracting it in anotherdimension, or certain areas of interest on the object could behighlighted and other areas de-emphasized by omitting such areasentirely or "graying them out".

From the foregoing, it will be seen that the present invention providesa method for the production of a three-dimensional image which iswell-adapted to the imaging of virtual objects and which can be effectedwithout the need to make a real copy of the virtual object. The presentmethod does not require elaborate apparatus or time-consuming multipleexposures, and preferred variants of the invention allow the use ofspecial techniques to ensure accurate registration of the image with thelenticular screen.

We claim:
 1. A method for printing an image on a lenticular sheet inregistration with the lenticles thereof, the image comprising aplurality of image areas each of which is to be printed in register witha lenticle of the lenticular sheet, the method comprising:providing, onthe surface of the lenticular sheet remote from the lenticles, aradiation-sensitive layer, the radiation-sensitive layer being sensitiveto radiation of a first wavelength but essentially insensitive toradiation of a second wavelength; directing a first beam of radiation ofthe second wavelength on to the surface of the lenticular sheet bearingthe lenticles, thereby causing this first beam to pass through thelenticular sheet, and detecting the periodic variation of the radiationon the side of the lenticular sheet bearing the radiation-sensitivelayer; scanning a second beam of radiation of the first wavelength overthe radiation-sensitive layer without passing the second beam throughthe lenticles of the lenticular sheet while modulating the intensity ofthe second beam, thereby imagewise exposing the radiation-sensitivelayer to produce the image, the modulation of the second beam beingcontrolled in dependence upon the detected periodic variation so thateach image area of the image is formed in register with a lenticle ofthe lenticular sheet.
 2. A method according to claim 1 wherein theradiation-sensitive layer comprises a color-forming composition adaptedto undergo a change of color upon increase in the temperature of theradiation-sensitive layer above a color-forming temperature for acolor-forming time.
 3. A method according to claim 2 wherein thecolor-forming composition comprises a material selected from:a. anorganic compound capable of undergoing, upon heating, an irreversibleunimolecular fragmentation of at least one thermally unstable carbamatemoiety, this organic compound initially absorbing radiation in thevisible or the non-visible region of the electromagnetic spectrum, saidunimolecular fragmentation visibly changing the appearance of theorganic compound; b. a substantially colorless di- or triarylmethaneimaging compound possessing within its di- or triarylmethane structurean aryl group substituted in the ortho position to the meso carbon atomwith a moiety ring-closed on the meso carbon atom to form a 5- or6-membered ring, said moiety possessing a nitrogen atom bonded directlyto said meso carbon atom and said nitrogen atom being bound to a groupwith a masked acyl substituent that undergoes fragmentation upon heatingto liberate the acyl group for effecting intramolecular acylation ofsaid nitrogen atom to form a new group in the ortho position that cannotbond to the meso carbon atom, whereby said di- or triarylmethanecompound is rendered colored; c. a colored di- or triarylmethane imagingcompound possessing within its di- or triarylmethane structure an arylgroup substituted in the ortho position to the meso carbon atom with athermally unstable urea moiety, said urea moiety undergoing aunimolecular fragmentation reaction upon heating to provide a new groupin said ortho position that bonds to said meso carbon atom to form aring having 5 or 6 members, whereby said di- or triarylmethane compoundbecomes ring-closed and rendered colorless; d. in combination, asubstantially colorless di- or triarylmethane compound possessing on themeso carbon atom within its di- or triarylmethane structure an arylgroup substituted in the ortho position with a nucleophilic moiety whichis ring-closed on the meso carbon atom, and an electrophilic reagentwhich upon heating and contacting said di- or triarylmethane compoundundergoes a bimolecular nucleophilic substitution reaction with saidnucleophilic moiety to form a colored, ring-opened di- or triarylmethanecompound; e. a compound of the formula ##STR17## wherein M' has theformula: ##STR18## wherein R is alkyl; --SO₂ R¹ wherein R¹ is alkyl;phenyl; naphthyl; or phenyl substituted with alkyl, alkoxy, halo,trifluoromethyl, cyano, nitro, carboxy, --CONR² R³ wherein R² and R³each are hydrogen or alkyl, --CO₂ R⁴ wherein R⁴ is alkyl or phenyl,--COR⁵ wherein R⁵ is amino, alkyl or phenyl, --NR⁶ R⁷ wherein R⁶ and R⁷each are hydrogen or alkyl, --SO₂ NR⁸ R⁹ wherein R⁸ and R⁹ each arehydrogen, alkyl or benzyl; Z' has the formula: ##STR19## wherein R' ishalomethyl or alkyl; X is --N═, --SO₂ -- or --CH₂ --; D taken with X andM' represents the radical of a color-shifted organic dye; q is 0 or 1;and p is a whole number of at least 1; said Z' being removed from saidM' upon the application of heat to effect a visually discernible changein spectral absorption characteristics of said dye; f. a substantiallycolorless di- or triarylmethane compound of the formula: ##STR20##wherein ring B represents a carbocyclic aryl ring or a heterocyclic arylring; C₁ represents the meso carbon atom of said di- or triarylmethanecompound; X represents --C(═O)--; --SO₂ -- or --CH₂ -- and completes amoiety ring-closed on said meso carbon atom, said moiety including thenitrogen atom bonded directly to said meso carbon atom; Y represents--NH--C(═O)--L, wherein L is a leaving group that departs upon thermalfragmentation to unmask --N═C═O for effecting intramolecular acylationof said nitrogen atom to open the N-containing ring and form a new groupin the ortho position of ring B that cannot bond to said meso carbonatom; E is hydrogen, an electron-donating group, an electron-withdrawinggroup or a group, either an electron-donating group or anelectron-neutral group that undergoes fragmentation upon heating toliberate an electron-withdrawing group; s is 0 or 1; and Z and Z' takenindividually represent the moieties to complete the auxochromic systemof a diarylmethane or triarylmethane dye when said N-containing ring isopen, and Z and Z' taken together represent the bridged moieties tocomplete the auxochromic system of a bridged triarylmethane dye whensaid N-containing ring is open; g. a colorless precursor of a preformedimage dye substituted with (a) at least one thermally removableprotecting group that undergoes fragmentation from said precursor uponheating and (b) at least one leaving group that is irreversiblyeliminated from said precursor upon heating, provided that neither saidprotecting group nor said leaving group is hydrogen, said protecting andleaving groups maintaining said precursor in its colorless form untilheat is applied to effect removal of said protecting and leaving groupswhereby said colorless precursor is converted to an image dye; h. mixedcarbonate ester of a quinophthalone dye and a tertiary alkanolcontaining not more than about 9 carbon atoms i. a leuco dye representedby: ##STR21## wherein: E represents a thermally removable leaving group;tM represents a thermally migratable acyl group; Q, Q' and C takentogether represent a dye-forming coupler moiety wherein C is thecoupling carbon of said coupler moiety; and, (Y) taken together with Nrepresents an aromatic amino color developer, one of said Q, Q' and (Y)containing an atom selected from the atoms comprising Group 5A/Group 6Aof the Periodic Table, said groups E and tM maintaining said leuco dyein a substantially colorless form until the application of heat causessaid group E to be eliminated from said leuco dye and said group tM tomigrate from said N atom to said Group 5A/Group 6A atom thereby forminga dye represented by: ##STR22## wherein said dotted lines indicate thatsaid tM group is bonded to said Group 5A/Group 6A atom in one of said Q,Q' and (Y).
 4. A method according to claim 1 wherein the firstwavelength in the range of from about 700 to about 1200 nm, and thesecond wavelength is in the visible region.